Vco Hybrid Assembly; No Or Low Output Power (Tx Or Rx Injection); No Or Low Modulation; Uhf Band - Motorola ASTRO Digital Spectra Service Manual

Troubleshooting Procedures: VCO Procedures
Mode AUX 1 AUX 2
VHF RANGE 1
RX HIGH HIGH
RX LOW HIGH
TX LOW HIGH
TX HIGH LOW
TX LOW LOW
VHF RANGE 2
RX HIGH HIGH
RX LOW HIGH
TX LOW HIGH
TX HIGH LOW
TX LOW LOW

4.3.1.3 No or Low Output Power (TX or RX Injection)

Use the test cables listed in the Service Aids section in the ASTRO Digital Spectra and Digital
Spectra Plus Mobile Radios Basic Service Manual (68P81076C20). Measure the power at the
synthesizer feedback port - if it is not within the range specified in the block diagram, troubleshoot
the first buffer. If failure is found in the first buffer, replace the defective component. If no failure is
found in the first buffer and the level out of the VCO (measured with an RF millivoltmeter) is below
that indicated in the block diagram, then replace the VCO assembly.
If the level at the synthesizer feedback port is within the indicated range, then troubleshoot the
divider, RX, and TX buffer.

4.3.1.4 No or Low Modulation

Under standard test conditions with a 1 kHz tone injected and 4.5 kHz (±50OHz) deviation, there
should be at least 0.8-V peak-to-peak present on J601, pin 10 (modulation input). (See the circuit
board overlay for location.) If this level is not present, troubleshoot the audio circuitry, if it is present,
check the VCO modulation circuitry.
4.3.2

UHF Band

Use these instructions along with the Theory of Operation, the VCO block diagram, and the
schematic to help isolate failures, first to the individual circuits, and finally to the failing piece part.

4.3.2.1 VCO Hybrid Assembly

The VCO hybrid substrate is glued to the carrier board. The hybrid is not a field-repairable assembly.
If a failure is indicated in this assembly, replace the complete hybrid. You will need a hot air source
for heating and softening the glue to separate the hybrid from the carrier board. If no hot air source is
available, replace the entire carrier board.
68P81076C25-C

Table 4-7. VCO Frequency

Radio Freq (MHz) VCO Freq (MHz)
136.00 - 158.35
158.35 - 162.00
136.00 - 145.20
145.20 - 157.00
157.00 - 162.00
146.00 - 166.15
166.15 - 174.00
146.00 - 150.00
150.00 - 162.00
162.00 - 174.00
Port Freq (MHz)
245.65 - 268.00 245.65 - 268.00
268.00 - 271.65 268.00 - 271.65
272.00 - 290.40 136.00 - 145.20
290.40 - 314.00 145.20 - 157.00
314.00 - 324.00 157.00 - 162.00
255.65 - 275.80 255.65 - 275.80
275.80 - 283.65 275.80 - 283.65
292.00 - 300.00 146.00 - 150.00
300.00 - 324.00 150.00 - 162.00
324.00 - 348.00 162.00- 174.00
4-15
Port
(RX)
(RX)
(TX)
(TX)
(TX)
(RX)
(RX)
(TX)
(TX)
(TX)
July 1, 2002